1. Field of the Invention
The present invention is related to an automatic power controlling apparatus to be used, for example, with an optical disk apparatus.
2. Discussion of Background and Other Information
When playing back data from an optical disk apparatus, a laser beam, having a comparatively low intensity, is incident to an optical disk. On the other hand, when recording data, a laser of a higher intensity than that used during playback is necessary to effect a change in the optical characteristics of the optical disk, so as to form pits thereon. Meanwhile, a semiconductor laser which serves as a light source of the laser beam cannot be driven with a constant current because of threshold current variations in the laser with temperature. When playback and recording operations are repeatedly performed, the temperature of the light sources varies, causing variations in the playback signal level. In addition, various servo systems become unstable. Furthermore, the recording power, which is adjusted to an optimum level, is varied, resulting in recordings with an inadequate intensity and deterioration of the signal-to-noise ratio during playback. To preclude the above defects, an automatic power controlling apparatus is provided.
In a prior art automatic power controlling apparatus, two reference intensity levels are provided for playing back and recording data. During playback, the laser beam intensity is controlled to a first reference level. During recording, the laser beam intensity is controlled to the first reference level and a second reference level, respectively, in accordance with the recording data in a high frequency.
Since, in the prior art apparatus, the laser beam power is controlled by two reference levels, the construction is complicated and the apparatus is expensive.